VideoObject (schema.org)
The schema.org type VideoObject marks up video content in structured form, with a title, description, thumbnail, duration and publication date for example, and thereby makes video rich results and video previews in search possible.
In practice
It is particularly effective in combination with complete subtitles or transcripts, since these improve both how well Google can index the content and how accessible the video is for users. Correct thumbnailUrl and uploadDate values also matter, because Google uses them for the presentation in search and in Discover-style surfaces.